Theories

Piaget theory of cognitive development 

Explains how a child constructs a mental model of the world. He disagreed with the idea that intelligence was a fixed trait, and regarded cognitive development as a process which occurs due to biological maturation and interaction with the environment. 

Piaget was the first psychologist to make a systematic study of cognitive development. His contributions included a stage of theory of child cognitive development, detailed observational studies of cognition in children, and a series of simple but ingenious tests to reveal different cognitive abilities. 

He was interested in fundamental concepts like the idea of number, time, quantity, causality, justice, and so on emerged rather than in how they count, spell or solve problems. 

Piaget was the first psychologist to make a systematic study of cognitive development. His contributions included a stage of theory of child cognitive development, detailed observational studies of cognition in children, and a series of simple but ingenious tests to reveal different cognitive abilities.

He was interested in fundamental concepts like the idea of number, time, quantity, causality, justice, and so on emerged rather than in how they count, spell or solve problems. 

Vygotsky sociocultural theory of cognitive development 

Vygotsky assumes cognitive development varies across culture.

Vygotsky states cognitive development stems from social interactions from guided learning within the zone of proximal development as children construct knowledge.

Cognitive development results from an internalization of language.

Adults transmit their culture’s tools of intellectual adaptation that children internalize.  

Erikson's stages of psychological development 

Personality develop through eight stages of psychological development, from infancy to adulthood. During each stage the person experiences a psychological crisis which would have a positive or negative outcome from personality development.

According to the theory, successful completion of each stage results in a healthy personality and the acquisition of strengths.

Failure to successfully complete a stage of result in a reduce ability to further stages and therefore a more unhealthy personality and sense of self. These stages can be resolved successfully later time.